(K-capture) An unstable atom with too many protons in the nucleus, and not enough energy to emit a positron, reaches a stable state in the way, that one proton captured an electron from the atom's inner shell (K-shell) and change to a neutron. A neutrino is emitted from the atoms nucleus by this process. The atomic mass of the atom is unchanged, but the decreased number of protons transformed the atom to a different element.

Image quality is an important value of all radiographic imaging procedures. Accurate measures of both image quality and patient radiation risk are needed for effective optimization of diagnostic imaging. Images are acquired for specific purposes, and the result depends on how well this task is performed. The imaging performance is mainly influenced by the imaging procedure, examined object, contrast agents, imaging system, electronic data processing, display, maintenance and the operator. Spatial resolution (sharpness), contrast resolution and sensitivity, artifacts and noise are indicators of image quality.
A high image contrast provides the discrimination between tissues of different densities.
The image resolution states the distinct visibility of linear structures, masses and calcifications.
Noise and artifacts degrade the image quality. In computed tomography (CT), high spatial resolution improves the visibility of small details, but results in increased noise. Increased noise reduces the low contrast detectability. Noise can be reduced by the use of large voxels, increased radiation dose, or an additional smoothing filter, but this type of filter increases blurring.
An image acquisition technique taking these facts into account maximizes the received information content and minimizes the radiation risk or keeps it at a low level.

See also As Low As Reasonably Achievable.

Isobars are atoms with equal mass number but different atomic number.

Isotopes of a given element have the same number of protons but a different number of neutrons in the core. Isotopes have the same electronic structure as the given element and thus have a nearly identical chemical behavior. Larger elements tend to have more stable isotopes than smaller ones.
For example, I123, I125 and I131 are isotopes of iodine; they have a different mass number.

A neutron (see also baryon) is a fundamental component of a nucleus. Neutrons, discovered by James Chadwick in 1935 (Nobel Prize in physics), have no charge and are about 1838 times more massive than electrons.

See also Neutron Activation, Neutron Activation Analysis, Neutron Radiation and Neutron Capture.